For these different applications, the radiating elements must be able to be excited in a compact manner in single or in dual polarization, to operate for high RF powers, and to have a bandwidth compatible with the intended application. Furthermore, the radiating elements used in the multibeam focal plane array antennas operating in low frequency bands must have a high surface efficiency, a small size, and a low weight. The radiating elements for array antennas have an integration objective which requires the provision of a very compact splitter.
For high-power, low-frequency applications, the radiating elements used are generally metal horns. However, these horns are very bulky and have a substantial weight.
An alternative solution to the metal horn is described in document FR 2959611. This solution relates to a compact radiating element made up of a stack of two Fabry-Perot cavities, which reduces the height of the radiating element by 50% compared with a compact metal horn. However, this radiating element is limited to an aperture diameter of less than 2.5λ, where λ represents the central wavelength, in a vacuum, of the frequency band used.
Planar antennas comprising micro-strip radiating elements enable effective distribution of the RF signals over a radiating aperture. Through the association of metal cavities, a stack made up of a spacer and a thin dielectric substrate, and micro-strip circuits, it is possible to obtain low-loss planar elements. However, these antennas are limited in power.
Planar antennas with apertures greater than 10λ generally comprise a splitter in waveguide technology to route the RF signal over great lengths and a splitter in micro-strip technology to distribute the RF signal locally to radiating elements. The RF signals are divided within the splitter in waveguide technology, and the power at the output of this splitter is often reduced, thus enabling finalization of the distribution of the signal to the radiating elements by a splitter in micro-strip technology. However, when the radiating surface is very small, for example in the region of several wavelengths, this hybridization of the waveguide and micro-strip technologies may not be possible. In fact, the first splitter in waveguide technology is too large and does not allow the distribution of the radiating energy over a very small surface.